Synthesis gas produced from different kinds of carbonaceous material such as wood chips, wood waste and various forms of biomass, including municipal and other wastes by a gasifier is utilized in combined heat and power plants (CHP plants) for generation of heat and electricity. One type of such plant raw synthesis gas is produced by burning carbonaceous material under oxygen limited environment in a gasifier after which the temperature of the hot raw gas is reduced in a heat exchanger, cleaned in a filtration unit and/or cyclone before utilization as a fuel for an internal combustion engine to produce electricity. In present CHP plants it is not possible to produce pure heat because the raw gas need to be always used for generating electricity by means of an internal combustion engine.
In known CHP plants the excess synthesis gas is typically burnt in a flare burner which is placed next to the gasifier. A drawback of such arrangement is that harmful emissions is formed by burning the raw gas containing incombustible contamination. Furthermore, in such plant there has to be at least two exhaust gas ducts; one for the raw gas burner and the other for the internal combustion engine.